Flaw detector

ABSTRACT

Flaw detection apparatus includes an electrode disposed in a region surrounded by a packaging material including a layer of an electrically-conductive material; a cutting member made of an electrically-conductive material and adapted to cut a predetermined portion of the packaging material; a variable detector, disposed between the electrode and the cutting member, for detecting an electrical variable; and flaw detection processor for reading the detected variable and for determining, on the basis of the detected variable, a flaw in the packaging material. In this case, the variable detector is disposed between the electrode and the cutting member.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 371 of PCT/JP01/11432 filed Dec. 27, 2000and claims priority under 35 USC 365 of Japanese Application No.2000-399148 filed Dec. 26, 2001.

TECHNICAL FIELD

The present invention relates to a flaw detection apparatus.

BACKGROUND ART

Conventionally, liquid foods such as milk and other beverages have beensold while accommodated within, for example, packaging containers formedfrom a packing material having a paper substrate. Examples of suchpackaging containers include polyhedral packaging containers andbrick-shaped packaging containers each having a flat top wall. Of thesepackaging containers, packaging containers having a capacity whichenables a purchaser to drink liquid food in a single serving are formedthrough a process of longitudinally sealing a web-shaped packagingmaterial into a tubular shape, transversely sealing and cutting thetube-shaped packaging material at predetermined intervals to therebyform initial-shape containers, and processing the initial-shapecontainers to complete the packaging containers. Further, a dischargeopening is formed in the top wall of each packaging container and iscovered with a pull tab from the outer side and with an inner seal fromthe inner side, and the pull tab and the inner seal are welded together.

During fabrication of the above described packaging container, heat isapplied to the packaging material, the pull tab, and the inner seal inorder to seal the packaging material in the longitudinal and transversedirections and to weld the pull tab and the inner seal together. At thattime, stress acts on resin layers which constitute the pull tab and theinner seal, respectively, possibly resulting in formation of flaws suchas pinholes and cracks in the packaging material. If such a flaw isgenerated in, for example, the innermost resin layer of the packagingmaterial, an aluminum foil layer, and the inner seal, the liquid foodcontained in the packaging container soaks into the paper substrate, andoozes from an end surface of the packaging material or from theinterface between the container body of the packaging container and thepull tab.

In view of the forgoing, there has been provided a flaw detectionapparatus which samples packaging containers at proper intervals; formsan opening in the top wall of each sampled packaging container; chargeswater into the packaging container; and immerses a portion of thewater-charged packaging container into water stored in a vessel. Sincean end surface of the aluminum foil layer is exposed to the outside ofthe packaging container, when electrodes are dipped in the water withinthe packaging container and the water within the vessel, respectively,electrical continuity is established between the two electrodes if apinhole has formed in the packaging container to a depth reaching thealuminum foil layer.

However, since the conventional flaw detection apparatus requires thelabor of charging water into each packaging container and partiallyimmersing the packaging container in water stored in the vessel, thelabor for flaw detection is cumbersome. Further, the flaw detectionapparatus cannot inspect all packaging containers. In addition, sincethe flaw detection apparatus forms an opening in the top wall ofpackaging containers to be inspected, the inspected packaging containersare destroyed.

An object of the present invention is to solve the problems involved inthe above described conventional flaw detection apparatus and to providea flaw detection apparatus which can simplify the labor necessary forflaw detection, which can inspect all packaging containers, and whichdoes not destroy the packaging container during inspection.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, a flaw detection apparatusaccording to the present invention comprises an electrode disposed in aregion surrounded by a packaging material including a layer of anelectrically-conductive material; a cutting member made of anelectrically-conductive material and adapted to cut a predeterminedportion of the packaging material; variable detection means, disposedbetween the electrode and the cutting member, for detecting anelectrical variable; and flaw detection processing means for reading thedetected variable and for determining, on the basis of the detectedvariable, a flaw generated in the packaging material.

In this case, since inspection for detecting a flaw in the packagingcontainer does not require charging water into each packaging containerand partially immersing the packaging container in water contained in avessel, the labor for flaw detection is simplified. Further, allpackaging containers can be inspected. Moreover, since no opening isformed in the top wall of each of packaging containers to be inspected,the packaging containers are not destroyed during inspection.

The flaw detection apparatus of the present invention may furtherinclude a sealing apparatus for sealing the packaging material; and thepredetermined portion of the packaging material is a seal formed by thesealing apparatus.

In the flaw detection apparatus of the present invention, the flawdetection processing means preferably reads the electrical variable atthe time when the cutting member cuts the seal.

In using the flaw detection apparatus of the present invention liquidfood may be charged into the region, and the electrode dipped in theliquid food.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a flaw detection apparatus according to anembodiment of the present invention;

FIG. 2 is a schematic view of a main portion of a charging machineaccording to the embodiment of FIG. 1; and

FIG. 3 is a block diagram of the flaw detection apparatus according tothe embodiment of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The embodiment of the present invention will next be described in detailwith reference to the drawings.

In the drawings, reference numeral 11 denotes a packaging materialformed from a flexible material; e.g., a laminate that includes a firstresin layer 12 made of polyethylene or like resin, an electricallyconductive aluminum foil layer 13, a paper substrate 14, and a secondresin layer 15 made of polyethylene or like resin, which are arranged inthis order from the inner side. When the packaging material 11 isunwound from a reel (unillustrated), the packaging material 11 assumes aweb-like shape. Subsequently, the packaging material 11 is sealedlongitudinally, while being transported, so as to form a longitudinalseal portion (unillustrated), whereby the packaging material 11 becomesa tubular packaging material; i.e., a tube T.

The tube T is continuously transported downward by means of a transferapparatus (unillustrated) and is nipped by two seal-cut units 16 (onlyone seal-cut unit 16 is shown in FIG. 2) at predetermined intervals,whereby the tube T is sealed transversely and a belt-shaped lateral sealportion S is formed. Each of the seal-cut units 16 includes a cuttingjaw 26 and a pressure jaw 27. A cutting bar 31 is disposed at the frontend (the right-hand end in FIG. 2) of the cutting jaw 26. An inductor 32serving as seal means is disposed at the front end (the left-hand end inFIG. 2) of the pressure jaw 27. By advancing both the cutting jaw 26 andthe pressure jaw 27 (moving the cutting jaw 26 rightward in FIG. 2 andthe pressure jaw 27 leftward in FIG. 2), the tube T is nipped from bothsides, so that opposing portions of the packaging material 11 arepressed against each other, and opposing portions of the first resinlayer 12 are welded. Thus, the tube T is sealed transversely.

A liquid food 17 is charged into the region surrounded by the packagingmaterial 11; i.e., within the tube T, from above. For this charging, acharge pipe 18, which is formed of an electrically conductive materialsuch as a metal and which serves an electrode, is inserted into the tubeT. The charge pipe 18 extends downward and has an open lower end. Theliquid food 17 is supplied from a liquid food supply source(unillustrated) to the charge pipe 18, so that the liquid food 17 isdischarged from the lower end of the charge pipe 18 into the tube T inthe direction of arrows B shown in FIG. 2. Thus, the lower end of thecharge pipe 18 is dipped in the liquid food 17 and is in electricalcontact with the liquid food 17. Although the charge pipe 18 is formedof a metal in the present embodiment, alternatively the charge pipe 18may be formed of an electrically conductive resin.

In order to maintain the liquid food 17 at a constant level within thetube T, there are provided: a float 21; an open/close valve 22 disposedwithin the charge pipe 18 for movement between an open position and aclosed position; and a link 23 which connects the float 21 and theopen/close valve 22. As the level of the liquid food 17 rises, the float21 moves upward, and the open/close valve 22 is closed by means of thelink 23 so as to stop charging of the liquid food 17. When the level ofthe liquid food 17 falls, the float 21 moves downward, and theopen/close valve 22 is opened by means of the link 23 so as to chargethe liquid food 17.

After completion of charging of the liquid food 17 and formation of thelateral seal portion S, the lateral seal portion S is cut in order toobtain an initial-shape container 25 containing a predetermined amountof the liquid food 17.

For such cutting operation, a horizontally extending flat cutter 33 isdisposed at the center of the cutting bar 31 in such a manner that thecutter 33′ can advance and retract (in the direction of arrow A). Whenthe cutter 33 is advanced (moved rightward in FIG. 2), the cutter 33cuts the tube T at a predetermined location (in the present embodiment,at the center of the lateral seal portion S) of the packaging material11. Specifically, an air cylinder 39, serving as an actuator, isdisposed at the rear end (the left-hand end in FIG. 3) of the cutter 33,and an operation medium such as compressed air is supplied from acompressed air source 38 via a changeover valve 40. Through supply andrelease of compressed air via the changeover valve 40, the cutter 33 canbe advanced and retracted. The changeover valve 40 assumes position A orB in accordance with a changeover signal from a control section 45. Atposition A, the changeover valve 40 supplies compressed air from thecompressed air source 38 to a chamber 39 a of the air cylinder 39, anddischarges compressed air from a chamber 39 b of the air cylinder 39. Atposition B, the changeover valve 40 supplies compressed air from thecompressed air source 38 to the chamber 39 b of the air cylinder 39, anddischarges compressed air from the chamber 39 a of the air cylinder 39.A groove 34 is formed in the inductor 32 so as to accommodate a tip endof the cutter 33 when the cutter 33 is advanced.

In FIG. 2, the seal-cut unit 16 is shown located in a seal-cut startposition, at which the cutting jaw 26 and the pressure jaw 27 areadvanced. Subsequently, the seal-cut unit 16 is moved downward (in thedirection of arrow B) while nipping the tube T, while the cutting bar 31and the inductor 32 are strongly pressed against the tube T, and theinductor 32 heats the aluminum foil layer 13 by means of inductiveheating. As a result, the opposed portions of the first resin layer 12are welded to thereby seal the tube T transversely. Although in thepresent embodiment the tube T is sealed by use of the inductor 32through inductive heating, the tube T may be sealed by use of a resistorwhich generates Joule heat.

Subsequently, the seal-cut unit 16 is moved further downward (in thedirection of arrow B), while cutting processing means (unillustrated) ofthe control section 45 causes the changeover valve 40 to assume positionA in order to advance the cutter 33 to thereby cut the lateral sealportion S at the-center thereof. Thus, a rectangular initial-shapecontainer 25 is separated from the tube T. The seal-cut unit 16 thenreaches a seal-cut end position.

Subsequently, the cutting processing means causes the changeover valve40 to assume position B in order to retract the cutter 33 andsimultaneously retract the cutting jaw 26 and the pressure jaw 27 (movethe cutting jaw 26 leftward in FIG. 2 and the pressure jaw 27 rightwardin FIG. 2). Subsequently, the seal-cut unit 16 is moved upward and thenmoved along the direction or arrow C to the seal-cut start position.

The initial-shape container 25, which has been formed in theabove-described manner, is transported to a forming machine(unillustrated), and is formed into a predetermined shape by the formingmachine, whereby a packaging container is obtained.

During fabrication of the above-described packaging container, becauseheat is applied to the packaging material 11 in order to seal thepackaging material 11 in the longitudinal and transverse directions,stress acts on the first resin layer 12, the second resin layer 15, andthe aluminum foil layer 13, which constitute the packaging material 11,possibly resulting in formation of flaws such as pinholes and cracks inthe packaging material 11. If such a flaw is formed in the first resinlayer 12 or the aluminum foil layer 13, the liquid food 17 contained inthe packaging container soaks into the paper substrate 14, and oozesfrom an end surface of the packaging material 11.

In view of the foregoing, the cutter 33 is formed of an electricallyconductive material such as a metal; and the charge pipe 18 and thecutter 33 are in electrical contact via a power source 41 and a currentsensor 43, which serves as variable detection means, in order to detectany flaw formed in the packaging material 11. Again, the electricallyconductive material may be an electrically conductive resin.

Current is detected by the current sensor 43 as an electrical variable,and a sensor output representing the detected current is fed to thecontrol section 45. At the time the cutting processing means causes thechangeover valve 40 to assume position A in order to cut the lateralseal portion S by means of the cutter 33, the flaw detection processingmeans of the control section 45 reads the sensor output fed from thecurrent sensor 43, and detects any flaw in the packaging material 11 onthe basis of the sensor output.

Thus, electrical continuity is established between the cutter 33 and thealuminum foil layer 13 when the advancing cutter 33 is cutting thelateral seal portion S at the center thereof. Therefore, when a flawsuch as pinhole or crack is formed in at least the first resin layer 12,electrical continuity is established between the liquid food 17 and thealuminum foil layer 13 at the location where the flaw has formed, sothat a closed loop is formed by the cutter 33, the current sensor 43,the power source 41, the charge pipe 18, the liquid food 17, and thealuminum foil layer 13, and current flows through the closed loop in thedirection of arrow D in FIG. 1, which current is detected by the currentsensor 43.

As described above, since the detection of a flaw in the packagingmaterial does not require charging water into each packaging containerand partially immersing the packaging container in water contained in avessel, the labor for flaw detection is simplified. Further, allpackaging containers can be inspected. Moreover, since an opening is notformed in the top wall of each of the packaging containers to beinspected, the packaging containers are not destroyed during inspection.

In the present embodiment, the current sensor 43 is used as the variabledetection means in order to detect current serving as the electricalvariable. However, as an alternative, a voltage sensor may be used asthe variable detection means in order to detect voltage as theelectrical variable.

In the present embodiment, the aluminum foil layer 13 is formed withinthe packaging material 11 and electrical continuity between the liquidfood 17 and the aluminum foil layer 13 at the location of a flaw isdetected. However, instead of the aluminum foil layer 13, a layer of anelectrically conductive material such as a metal (e.g., steel) or anelectrically conductive resin may be formed within the packagingmaterial 11, in which case electrical continuity between the liquid food17 and the electrically conductive material layer at the location of aflaw is detected.

In the present embodiment, the charge pipe 18 serves as an electrode.However, an electrode provided in the tube T separately from the chargepipe 18 may be dipped in the liquid food 17, in which case electricalcontinuity between the electrode and the cutter 33 via the power source41 and the current sensor 43 is established in order to detect a flawformed in the packaging material 11.

In the present embodiment, sealing and cutting are performedsimultaneously by the inductor 32 and the cutter 33, respectively.However, cutting may be performed after completion of sealing.

The present invention is not limited to the embodiments described above.Numerous modifications and variations of the present invention arepossible in light of the spirit of the present invention, and they arenot excluded from the scope of the present invention.

1. A flaw detection apparatus comprising: (a) an electrode disposeddipped into liquid food charged into a region surrounded by a packagingmaterial including a layer of an electrically-conductive material; (b) acutting member made of an electrically-conductive material and adaptedto cut a predetermined portion of the packaging material; (c) variabledetection means, disposed between the electrode and the cutting member,for detecting an electrical variable; and (d) flaw detection processingmeans for reading the detected electrical variable and for detecting, onthe basis of the detected electrical variable, a flaw generated in thepackaging material.
 2. A flaw detection apparatus according to claim 1,wherein (a) the flaw detection apparatus further comprises a sealapparatus for sealing the packaging material; and (b) the predeterminedportion of the packaging material is a seal portion formed by the sealapparatus.
 3. A flaw detection apparatus according to claim 1, whereinthe flaw detection processing means reads the detected electricalvariable at a time when the cutting member cuts a seal portion.